The purpose of this study is to investigate new digital imaging algorithms to be used in conjunction with a digital beam attenuator device (DBA) for improved digital radiography of the chest. Specifically, two algorithms are proposed: (1) a variable compensation mode, whereby the amount of image compensation is interactively selectable (but the image signal-to-noise remains optimized, and (2) a compensated dual-energy technique, which improves signal-to-noise in the tissue-cancelled image and eliminates image shading artifacts due to the beam attenuator. Both algorithms use the DBA to compensate the x-ray beam, and then add to the final compensated image a fraction of the low-dose attenuator-formation image. Proper signal-to-noise is maintained by blurring the low-resolution, low-dose attenuator-formation image prior to addition. Each algorithm will undergo phantom validation studies, after which a suitable system will be constructed for initial clinical investigation. This system will consist of a digital beam attenuator, image processing hardware and software, and a barium fluorohalide photostimulable digital detector. An additional key element of the system will be a dedicated low-dose digital detector for fabrication of the attenuating filters. This low-dose detector, comprised of a 64 x 64 matrix of very sensitive photodiodes, has recently been developed in our laboratory for application to both film-based and digital DBA chest radiography. The specific aims of this proposal include: (1) Design, implementation and evaluation of a new low-dose digital detector for DBA mask-image acquisition. (2) Construction of a DBA chest apparatus. (3) Investigation of a variable compensation algorithm for single-energy digital chest radiography with the DBA. (4) Investigation of a compensated dual-energy algorithm for improved tissue-cancelled digital chest imaging with the DBA.